1. Field of the Invention
This invention relates to a sound-source-search system that searches for a sound source such as acoustic noise, and more particularly to a sound-source-search system in which a plurality of microphones are arranged at locations on a spherical, semi-spherical or polyhedral baffle surface and/or location separated from the surface, and processes the electrical signals from the sounds obtained from each of the microphones, and estimates the direction from which the sound comes and intensity of the sound source from all directions.
In an electric generation plant, chemical plant, factory having an assembly line, or the like, acoustical noise that is generated from various equipment and machinery such as motors, pumps, fans, transformers, etc., are combined and reach bordering areas or nearby homes. Also, inside transportation means such as automobiles, trains, airplanes, acoustical noises that are generated by the various components such as engines, gears, fans, and the like are combined and inhibit silence inside. Moreover, in normal housing areas such as apartments, and the like, silence inside is inhibited by various noises. In order to solve the problems posed by these acoustical noises, it is necessary to accurately know the direction from which the sound is coming, and the intensity of the sound source.
Conventionally, a sound source was searched for by placing a plurality of microphones over a wide area, recording the acoustical signals obtained by way of those microphones by a recording device such as a tape recorder and processing each of the recorded acoustical signals. However, in this kind of method of searching for a sound source, not only was it necessary to set up a plurality of microphones over a wide area, it was also necessary to wire each of the microphones to a recording device, so the set up work was very complicated.
Also, as a different sound-source-search method is the sound-source-search apparatus disclosed, for example, in Japanese Patent Publication No. H06-113387. This is an apparatus that faces a parabolic reflector in the direction from which the sound is coming and records the acoustic signal to make it possible to visualize the sound source. However, the disadvantage of this method is that the estimated sound source is limited to the direction in which the parabolic reflector is faced. In other words, the recording direction is limited by the location and angle at which the microphone is located, so it is impossible to search for sound sources in all directions at the same time.
In order to solve this problem, in Japanese Patent Publication No. 2003-111183 a sound-source-search system is proposed in which a first to fourth microphone are arranged on a rotating frame that is installed on a base to form a detection unit with an origin point located in the center of a square XY plane, and a fifth microphone is placed above the center of the square formed by the first to fourth microphones such that the distances between the first to fourth microphones and fifth microphone are the same, and the direction from which the sound is coming is estimated from the difference in arrival time of output signals from each microphone.
However, in Japanese Patent Publication No. 2003-111183 described above, the first to fifth microphone are located on a rotating frame, and as can be analogized from the simplified installation work and a single-mounted camera, since it is necessary to rotate the rotating frame in order to search for a sound source in all directions, it is impossible to identify the direction from which the sound is coming and estimate the intensity of the sound source in all directions at the same time. Moreover, since the microphones, camera and accompanying cables are located in a naked state in the space through which the sound propagates, the system is vulnerable to the sound reflected from the microphones, camera and cables themselves, which has a large effect on the results of the search for the sound source.
Taking into consideration the problems described above, the object of this invention is to provide a sound-source-search system that is not limited to a small space and is capable of identifying the direction from which sound is coming and the intensity of the sound source in all directions at the same time.